There is a need remove hardness values, especially Mg.sup.++ and Ca.sup.++, from brines, especially NaCl solutions, where such brine is intended for uses in which the hardness values are detrimental. One notable use of NaCl brines is that wherein the brine is used as an electrolyte, e.g., as a feed material to an electrolysis cell, such as a chlorate cell or a chlor-alkali cell. Other brines include LiCl solutions, KCl solutions and other alkali metal brines.
The use of chelating-type ion exchange resins for removing hardness values from brine is disclosed, for example, in U.S. Pat. Nos. 4,060,465 and 4,119,508. Other patents disclosing brine treatment are, e.g., U.S. Pat. Nos. 4,405,574; 4,405,576; 4,415,678; and 4,415,677.
Ethylene polymerized with unsaturated organic carboxylic acids, e.g., acrylic acid, to form copolymers is taught, e.g., in U.S. Pat. Nos. 2,391,218; 3,520,861 and 4,351,931. Copolymers of ethylene and such acids can be made by grafting the acid onto polyethylene, by batch or continuous polymerization of mixtures of monomers of ethylene and the acid, by polymerization of mixtures of monomers of ethylene and the acid in a tubular reactor, and by hydrolysis of copolymers of ethylene/alkyl acrylates which converts the ester groups to carboxylic acid groups. Also, block copolymers can be made whereby chain segments of polyacrylic acid and chain segments of polyethylene form long polymer chains. Any of these known ethylene/acid copolymers are at least somewhat usable in the present invention, so long as they can be formed into solid particles, fibers or filaments. Thus, the purview of the present disclosure includes ethylenic polymers containing a plurality of carboxylic acid groups in their molecular structure, especially the homogeneous, compositionally uniform, random copolymers such as prepared in accordance with U.S. Pat. Nos. 3,520,861 and 4,351,931.
U.S. Pat. No. 3,801,551 is closely related in subject matter to the present invention, since it shows preparation of ethylene/unsaturated carboxylic acid copolymer (ECA) fibers; also U.S. Pat. Nos. 3,790,521 and 3,798,194 are related subject matter. Each discloses treatment of ethylenic polymers containing carboxylic acid groups with an alkaline material in order to obtain certain results, such as the making of fibers, non-colloidal particles, or colloidal particles by digesting particles of the polymers in an alkaline material, followed by shearing.
It has been more recently discovered that there are unexpected improvements resulting from a change in the known process of forming fibers of polymers such as ethylene/carboxylic acid copolymers (ECA), said known process being that of digesting particles of the polymer in alkaline material and then subjecting the so-treated polymer to shearing forces to cause fibrillation or particulation of the polymer particles. The said change in the process involves, as the principal distinguishing feature, the orientation (i.e. "stretching") of the polymer (before treating with a reagent) at a temperature below that at which stress-relaxation of the stretched polymer molecules is substantially encountered; this may be referred to as "cold-stretching" or "crystalline orientation".
It is customary, in some production processes, for polymers leaving a polymerization vessel to be melt-extruded through a die as strands, which are chopped into pellets and cooled in a water bath. U.S. Pat. No. 3,801,551 discloses that such pellets may then be digested in alkaline material and then fibrillated using shearing forces. Since the strands are cut into pellets before the strands have cooled to the point at which crystallization occurs, the stress relaxation of the polymer molecules permits intertwining of the molecules. When such pellets are treated in accordance with U.S. Pat. No. 3,801,551 to prepare fibers, the fibers are relatively short and have very little porosity, if any. Polymers produced as small particles may also be melted, extruded as strands, and chopped into pellets before the intended end-use.
It has been found that if the extruded strands of polymer are allowed to cool to an extent, and for a time, sufficient to allow an appreciable amount of crystallization to occur and are then cold-stretched (oriented), the crystallized molecules become substantially untwined and become substantially aligned in parallel relationship with the direction of orientation. This also draws the strands to narrower dimensions. Since the polymer, when oriented, is cold enough for the molecules to be crystallized, and not warm enough to allow stress-relaxation of the molecules, then the molecules remain dimensionally stable after the orientation is completed. When these oriented strands are treated with a reagent (e.g. 0.5N NaOH) and subjected to shearing or crushing, the strands undergo fibrillation into fibers which are extensively porous. Most of the pores are small enough to be considered micropores. These micropores permeate the length and breadth of the fibers. Even if the oriented strands are chopped into pellets before being treated with alkali and subjected to shearing or crushing, the so-formed fibers are extensively porous and are longer than fibers prepared from pellets of the same dimensions treated in accordance with U.S. Pat. No. 3,801,551.
This same phenomenon is observed when cold oriented films or strips are treated with alkali and sheared or crushed into fibers, and to a greater degree than when using films which are stretched at high temperatures where stress relaxation of the polymer molecules is possible. These recently discovered highly porous fibers and particles are the subject of co-filed patent application Ser. No. 776,534, filed on even date herewith. These highly porous fibers and/or particles are especially preferred due to their high efficiency in scavenging metal ions.